Ovarian follicles transplanted under the kidney capsule are known to luteinize in response to endogenous or exogenous luteinizing hormone. This technique will be used to study various materials for luteotropic or luteolytic properties, in order to more clearly define the physiological mechanism of luteal function. Preliminary results in our laboratory indicate that in vivo luteal tissue formed under the kidney capsule respond quite differently in rats that are ovariectomized-hysterectomized with or without hypophysectomy than do luteal cells in tissue culture. Transplantation of follicles will be made under the kidney capsule of rats following various surgical preparations and treatments applied. Function of the transplant will be followed by assaying peripheral plasma for progesterone and degree of luteinization determined in histological preparations of the transplant.